Shrub removal effects on runoff and sediment transport in a mediterranean experimental catchment (Vernegà River, NE Spain)

Shrub removal works in the Gavarres massif (NE Spain) have impacted runoff and sediment transport in a first-order experimental catchment (2.5 km2), named Vernegà. These works have consisted in removing the shrub layer that grows under a typical mixture of cork oak tree and Mediterranean pine forest, and have been undertaken regularly since 2002 to reduce risk of forest fire and increase cork oak productivity. In 2005, the works affected the catchment headwaters, resulting in significant changes in runoff and sediment transport rates. This study aimed to assess short-term changes in runoff and sediment transport rates in the experimental catchment by comparing them to rates prior to 2005. Measurements were made at two monitoring stations within the basin: i) Bosc (1.6 km2), where the main land use is forest; and ii) Campàs (2.5 km2), the catchment outlet, where the main land use is agriculture.Mean annual runoff increased from 11.7 mm before 2005 to 33.1 mm after 2005 at the Bosc station. At the Campàs station, runoff increased from 81.9 mm to 92.2 mm. These changes can be observed in the flow duration curves of both stations. An increase on the frequency when low flows (<5 l/s) take place has been observed, while the occurrence of high flows remains unchanged. The low flow increase period had a concomitant reduction of the no flow period, which reduced about 30 days in Bosc station.Suspended sediment yield increased from 250 kg·km−2·yr−1 at Bosc and 430 kg·km−2·yr−1 at Campàs to 940 kg·km−2·yr−1 and 4,350 kg·km−2·yr−1 respectively after forest works. Dissolved sediment yield also increased but did so solely as a result of the increase in runoff rates rather than of the increase in dissolved concentrations

Runoff and erosion generation by simulated rainfall in a Mediterranean forest with forest management

Introduction: Forest management is necessary for forest conservation and the security of natural assets and people; however, forest management can have negative effects on some soil properties. Objective: To determine whether forest management in a Mediterranean forest basin, consisting of Quercus suber L. and Pinus halepensis Mill., causes increased runoff and eroded material at slope level. Materials and methods: Seven land-use units were selected: a) dense forest (no management); b) recently managed cork oak forest, c) recently managed pine forest; d) cork oak forest with two years of management, e) pine forest with two years of management, f) bare terrain with herbaceous vegetation and (g) a forest road. In each area, four rainfall simulations were carried out from a height of 2 m, at a pressure of 1.7 kg·cm -2 , equivalent to a rainfall intensity of 60 mm·h -1 . An ANOVA was performed and significant differences were verified (post-hoc Tukey test, P < 0.05). Results and discussion: The forest road and the bare terrain, areas devoid of vegetation, produced more runoff (4 to 12 %) than more vegetated areas (<1 %). The forest road recorded significantly higher erosion values (96 g·m -2 ) than the other land uses (<4 g·m -2 ) Conclusion: There is no difference in the generation of runoff and erosion in the managed areas, both pine and cork oak, compared to dense or unmanaged forest

Relationship of runoff, erosion and sediment yield to weather types in the Iberian Peninsula

Precipitation has been recognized as one of the main factors driving soil erosion and sediment yield (SY), and its spatial and temporal variability is recognized as one of themain reasons for spatial and temporal analyses of soil erosion variability. The weather types (WTs) approach classifies the continuumof atmospheric circulation into a small number of categories or types and has been proven a good indicator of the spatial and temporal variability of precipitation. Thus, themain objective of this study is to analyze the relationship betweenWTs, runoff, soil erosion (measured in plots), and sediment yield (measured in catchments) in different areas of the Iberian Peninsula (IP) with the aimof detecting spatial variations in these relationships. To this end, hydrological and sediment information covering the IP from several Spanish research teams has been combined, and related with daily WTs estimated by using the NMC/NCAR 40-Year Reanalysis Project. The results showthat, in general, a fewWTs (particularly westerly, southwesterly and cyclonic) provide the largest amounts of precipitation; and southwesterly, northwesterly and westerly WTs play an important role in runoff generation, erosion and sediment yield as they coincide with the wettest WTs. However, this study highlights the spatial variability of erosion and sediment yield in the IP according to WT, differentiating (1) areas under the influence of north and/or north-westerly flows (the north coast of Cantabria and inland central areas), (2) areas under the influence of westerly, southwesterly and cyclonic WTs (western and southwestern IP), (3) areas in which erosion and sediment yield are controlled by easterly flows (Mediterranean coastland), and (4) lastly, a transitional zone in the inland northeast Ebro catchment,wherewe detected a high variability in the effects ofWTs on erosion. Overall results suggest that the use of WTs derived fromobserved atmospheric pressure patterns could be a useful tool for inclusion in future projections of the spatial variability of erosion and sediment yield, as models capture pressure fields reliably

Dinámica hidrológica y sedimentológica en una cuenca representativa mediterránea. Riera de Vernegà (1993-2012)

[spa] El objetivo principal es la cuantificación y relación de la precipitación, humedad del suelo, nivel de los acuíferos, escorrentía y el transporte de sedimentos en dos diferentes usos del suelo (agrícola y forestal), realizado en la cuenca de la riera de Vernegà. La exposición de resultados se divide en dos periodos, el primero desde 1993 2005 y el segundo de 2005 a 2012 con una clara influencia en la hidrología por la gestión forestal acaecida en la cuenca.[eng] The main objective of this study is the quantification and relation of precipitation, soil moisture, groundwater level, runoff and sediment transport in two different land uses (agriculture and forestry), conducted in the Vernegà basin. The presentation of results is divided in two periods, the first from 1993 to 2005 and the second from 2005 to 2012 with a clear influence of the forest management which took place at the beginning of the century on the hydrology of the basin